Challenges of cleaning up waste at a Cumbria nuclear site are "unprecedented" and more complex than "any other operational or decommissioning nuclear site in the world", the head of the team overseeing Sellafield nuclear site.
NMP chairman Tom Zarges dodged claims costs were spiralling out of control and said the consortium was focused on building on "our experience of the last five years".
The consortium overseeing the clean up of waste at Sellafield nuclear site has failed to meet taxpayer demand and the National Audit Office should review the management of the site, MPs have said.
The American-led management were accused of failing to train and keep staff to the detriment of the project, as well as planning a future for the site which "doesn't make sense".
The cost of cleaning up nuclear waste at Sellafield has soared to "astonishing" levels, with latest figures estimating the bill has already hit £70bn, according to a group of influential MPs.
The Public Accounts Committee (PAC) said the cost would continue to rise and blasted "poor" progress at the Cumbria site.
They also accused Nuclear Management Partners (NMP), who were brought in to manage the clean up, of letting timescales slip and running a project with "escalating" costs.
Among a series of recommendations MPs called on the Nuclear Decommissioning Authority (NDA) to terminate the contract with NMP if their performance did not improve.
The report said the consortium had been brought in six years ago to help Sellafield improve its performance and had its contract extended last October despite "spiralling costs and poor performance".
The World Nuclear Association, which promotes civil nuclear energy, reports that Sellafield has put the elevated radioactivity reading down to "variations in natural background".
Irish officials have been in contact with Britain over raised levels of radioactivity at the Sellafield nuclear reprocessing plant, the government has said.
Only around 112 miles (180km) separates the nuclear site from the coast of Ireland.
"Officials from the Department of the Environment have been in contact with their UK counterparts ... and will receive updates throughout the day," the Irish government said in a statement.
Professor Richard Wakeford, professor of epidemiology at the University of Manchester, has said that the level of radioactivity detected at Sellafield is not above that "encountered in everyday life".
The Nuclear Decommissioning Authority (NDA) has said it is too early to say whether there is a leak at the Sellafield site, but stressed that there was no danger to the public.
It added that it is still not clear where the radiation is coming from.
One Sellafield worker told the Press Association that an air sampler on a perimeter fence had detected a problem, which led to staff being told to stay away.
It is understood nothing has been detected inside the plant.